When you collect three painting bids on the same project and they come back at $3,200, $4,800, and $6,100, you have a comparison problem — not just a price problem. The numbers aren't necessarily measuring the same thing, because contractors bid in different structures that allocate risk and accountability very differently.
Understanding the three common bid structures doesn't require a construction background. It requires knowing which questions to ask before you sign.
Time-and-materials (T&M)
The contractor charges you their hourly labor rate — typically $60 to $100 per painter per hour in Portland — plus materials at cost or cost-plus a markup (10–25% is standard). The advantage is transparency: you're seeing real hours and real costs. The disadvantage is that you bear the risk of scope creep. If prep takes longer than expected or the crew runs slowly, you pay for those hours. T&M works well when scope is genuinely uncertain — e.g., stripping a room to bare plaster before painting — but for a defined project like "paint the exterior of this house," it puts you in the position of supervising a meter that's running.
Lump sum (fixed price)
The contractor gives you a single number for the completed project. The advantage is certainty — barring scope changes, you know what you're paying. The risk is that a vague scope statement can be interpreted narrowly. If the quote says "paint exterior — $4,500" and the contractor's definition of paint includes one coat of finish but not primer, or excludes trim, or assumes you'll do your own caulking, you'll be having those conversations mid-job. A well-written lump-sum quote is protective; a one-line lump-sum quote is a liability.
Unit pricing
The contractor prices by measurable unit — price per linear foot of trim, price per square foot of wall, price per door. This makes scope changes easy to price and compare and is common on larger residential and light commercial projects. For a whole-house repaint, most contractors will roll this up into a lump sum, but asking a contractor to show their unit pricing is a useful way to understand whether their lump sum is internally consistent.
What actually protects you
The bid structure that protects you most is a lump-sum quote with an itemized scope — each line of work described specifically enough that both parties agree on what "done" looks like. Separate lines for prep, prime, finish coat, and any repairs. A clear statement of what paint product is specified. A change order clause that requires written approval before proceeding with any scope addition.
When we write a TrueLine estimate, we break out every scope item so that you can see exactly what labor and materials are in the number. The total is fixed, but the components are visible. That combination — lump-sum certainty plus itemized transparency — is the structure that eliminates most of the disputes we've been called in to resolve after a competitor finished a job badly.